1. Field of the Invention
The present invention relates to a method for producing compounds, and more particularly to a method which can produce a high-quality compound having a predetermined stoichiometric composition.
2. Description of the Prior Art
Recently, a variety of compounds have been employed as electronic materials, for instance, semiconductors, magnetic materials, dielectrics and piezoelectric materials. The advent of these electronic materials made of compounds has made it possible to develop sophisticated devices or elements having new and novel characteristics. For instance, in the field of semiconductors, element semiconductors consisting singly of silicon, germanium or the like were exclusively used in the beginning. However, compound semiconductors consisting of at least two kinds of elements such as of Groups II and VI or Groups III and V have been recently developed and put into practical use as light-emitting diodes, semiconductor lasers, and the like.
The compound semiconductors of the kind mentioned above have great advantages in that the band gap or energy gap thereof can be freely changed by changing the kinds and proportions of the component elements thereof. Therefore, the light-emitting diode can be made to emit light of any wavelength in the range from red to green. Also, the compound semiconductors are very high in electron mobility and are being put into practical use as ultra high frequency devices, microwave solid-state oscillators, laser oscillators, and the like.
In the conventional physical evaporation processes such as vacuum deposition and ion plating, the compound semiconductors were produced by, for instance, vaporizing and depositing the component elements in a low-pressure gaseous atmosphere or in a vacuum region. Each of these processes however, has the following disadvantages.
In order to produce a compound having a stoichiometric composition, a special apparatus and complicated operations are required because the component elements of the compound are different in chemical and thermodynamic properties from one another.
In addition, the III-V compound semiconductor, for instance, is a high-melting-point compound and contains phosphorus (P) and arsenic (As) of Group V which are very high in vapor pressure. Therefore, when a substrate is heated to make the semiconductor epitaxially grow thereon, substances which are high in vapor pressure such as phosphorus and arsenic tend to escape therefrom. Thus, the conventional process cannot produce III-V compound semiconductors high in crystal quality unless the substrate is placed in a high-pressure atmosphere containing large amounts of phosphorus and arsenic.
Accordingly, in the case of the above-mentioned conventional process, it is necessary to supply phosphorus and arsenic more than other component elements so that phosphorus and arsenic that have been re-vaporized may be replenished. As a result, the yield of the product is very poor.
As mentioned above, the component elements of the compound semiconductor are widely different in melting point and vapor pressure from one another. Thus, when a high quality film is to be formed, the conventional process mentioned above encounters much difficulties in controlling the temperature of the crucible for vaporizing the materials of the film and in homogeneously mixing two or more component elements of the film, which requires very complicated operations.